The Grind-R-Lap -- A Low Speed Diamond Grinder

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Diamond is the hardest known material so it is an obvious choice for grinding and is often used to grind carbide tooling. Diamond wheels are not recommended for grinding HSS because the heat causes the diamond to dissolve in the steel. The way around this is to rotate the diamond wheel slowly to keep the heat low enough so the diamond isn't damaged. The Leonard Grind-R-Lap (shown above) was the first to commercialize this idea but the idea has been used by others since: Accu-Finish, Cold Grind, Enco, Eskimo, K-K Calamar, SPI, Victory and possibly others. Many of these companies, including Leonard, have ceased making these grinders although Accu-Finish continues to supply a version (plus wheels for the Leonard). Information on these great machines seems to be in short supply so here's a manual(11mb pdf); the following notes are from examining and using this machine.

The Leonard design is elegantly simple with a surprising economy of parts considering its capability. The diamond wheels are 5" diameter with a 3" hole, held to the spindle magnetically; this allows changing wheels/grits in seconds. Most wheels use plating to hold the diamond grit but composite wheels are also available. The 1" wide wheel oscillates sideways so when a tool is presented to the center of the plated area it actually uses the whole width; this avoids wearing grooves in the diamond abrasive.

The grinder is comprised of three major cast aluminum assemblies: the power unit, the case, and the table (shown at right, click to enlarge). The power unit mounts in the case on two bearings, one bearing is seen at the bottom of the power unit. This bottom view shows the sparse internals. The 1740 RPM motor is stepped down about 5:1 by the pulleys to provide a wheel RPM of about 350. The wobbulator is a small eccentric wheel, seen peeking out of its support in the top of the case; the spindle shaft rides on and drives this wheel so its eccentricity causes the grinding wheel to shift side-to-side about once per second. Gravity plus a small spring hold the spindle shaft against the wobbulator wheel.

The table tilt is quickly adjusted via the handle shown on the front of the case, referencing the degree scale on the right side. There are two handles on the right side of the case. The lower handle retracts the table away from the wheel to allow changing wheels. The upper handle is used to disable the wobbulator so small details can be ground easily. The upper handle is also used to relieve pressure on the wobbulator wheel so the spindle shaft doesn't leave an indent in its rubber surface while parked; just push the lever to the rear prior to turning power off - the lever then supports the power unit away from the wobbulator wheel until the unit is used again.

Diamond wheels are available in various grits from several sources. In addition, a lap can be used where a steel wheel has a brass face attached and diamond paste is used on this to lap cutting tools to a mirror finish. Owners also make steel wheels and glue fine carbide paper to them for a finish similar to a lap. Cutting lubricant, generally water based (but some owners suggest WD-40), is used with the plated diamond wheels to minimize loading and increase wheel life. Diamond wheels can be cleaned with scouring powder, water and a toothbrush.

Grind-R-Lap User Notes

The Grind-R-Lap spins its diamond wheel at low enough speed that it can grind HSS without damaging the wheel through heating. It is also effective on carbide and brazed carbide, where it can grind carbide and the supporting steel without harming the wheel, unlike most high speed diamond grinders.

It is less intimidating to use a Grind-R-Lap than a bench grinder because its low speed steel wheel can't fail catastrophically. Plus, it is a quiet machine to use and doesn't spray grit in the immediate area as typical bench grinders often do so it can be kept near other machines for easy access. Grinding residue generally falls down below the wheel and can be cleaned up easily because the feet provide clearance.

While a coarse (260 grit) diamond wheel cuts rapidly, rough grinding is generally done on a bench grinder followed by finish grinding on the Grind-R-Lap. A medium (600 grit) wheel is appropriate following the bench grinder; it leaves a nice finish and generally doesn't require further honing. When a finer finish is desired then a lap or carbide paper wheel is used. The hollow grind produced by the periphery of a bench grinder wheel can be refined very quickly on the Grind-R-Lap since only the cutting edge need be ground. Table tilt combined with a miter (not shown) allows grinding compound angles on bits.

I noted that after about 3 resharpenings on this unit, bits seem to remain sharp longer between resharpenings. My notion is that sharpening on a bench grinder overheats the cutting edge because there isn't enough material nearby to conduct the heat away. Resharpening on the low speed diamond eventually removes this damaged HSS so the real HSS characteristics return. Not easy to verify this is what's going on but my tangential and parting tools seem particularly improved.

Grind-R-Lap Maintenance Notes

The Grind-R-Lap is designed for easy maintenance but this may be neglected because it continues to work well with minimal care. To dismantle, unplug power then tip the unit back onto a towel (to protect the paint). The power unit is easily removed by disconnecting the spring pulling it toward the wobbulator wheel, then remove the rear threaded shaft that supports the power unit. The complete power unit can then be manuevered off the front support and placed beside the case - the power unit's cord is long enough to allow this.

The wobbulator wheel can be removed through the front of the case. The grease in the shielded ball bearing is often dried up; it is worth trying a little oil on the shield which may penetrate and free a frozen bearing. This worked on my unit and although it is clearly not perfect it now works fine and will likely go for quite a while because it only runs about 60 RPM. If this doesn't work out then it is a standard bearing and easily replaced. If the rubber tire on the wheel fails then a new tire must be fashioned since they aren't available. The wheel is 3/8" aluminum; the center of rotation is 1/8" from the wheel center.

The reversible motor needs occasional oiling according to its nameplate. The spindle bearings are shielded and could be replaced if they fail. It isn't clear how the spindle shaft is retained, it may simply be pressed into the bearings. Removal would be a learning experience :-) One source for replacement belts is McMaster-Carr.

The nut on the front power unit support had been backed off and not returned to what I assume is the correct position. This nut rusted onto the threads from liquid used on the wheel so I had to turn it down until the threads would peel off, then run a die over the 1/2-20 threads. I made two nylon nuts for the front and rear supports. Although there wasn't a nut on the rear support I felt there should be one because the wobble turned the support on its threads rather than pivoting on the bronze bearings. I used these nylon nuts to lock the supports to the case with the idea that the nylon wouldn't rust in place as the original nut did. Although grease is normally not used on grinders, I added a dab to the bearings supporting the power unit. The front support sets the clearance between the wheel and the table so thread it through until the wheel clears the table when the table is in its forward position. The rear support is spring loaded to accommodate this.

I removed the unit's table to re-paint; this required tapping the table's pivot pins out from the inside after removing the power unit. Some versions of the Grind-R-Lap use bolts instead of pivot pins so this can vary. Note that the table springs are right and left handed.

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